In cold-drawing wire, the diameter of the wire is reduced as it is pulled through a circular die. Dry lubricants, usually different kinds of soaps or fats, are applied between the wire and the die. These lubricants wet the surface of the wire and the die for decreasing the drawing force, die wear, and drawing temperature, all of which improve the quality of the drawn wire. Traditionally, dry lubricants, like powder or other granulated material, are loaded into a soapbox or similar container which is situated in front of the die. The lubricant is fed to the die by direct application to the surface of the wire which moves the lubricant into the die as the wire is drawn through. As a rule, the frictional forces between the lubricant and the wire are not adequate for feeding sufficient lubricant to the die by direct mechanical application. Frictional application forces against the wire are further reduced because sometimes the wire makes a channel in the dry lubricant reducing the contact friction and, hence, the lubricant feed to the die is further reduced.
There are many known methods to enhance feeding dry lubricant to the die, or applying it to the wire to carry the lubricant to the die. The most commonly used technique is the preliminary coating of the wire surface by materials, such as lime, borax or phosphate applied ahead of the soapbox which can improve the adhesion between the wire surface and the dry lubricant. Other attempts to improve wire lubrication include the mechanical feed of the dry powdered lubricant into the die by a power-driven, screw-type feeder located in the soapbox. Other methods employed to enhance the lubrication of the wire and the die also include mechanically coating the surface with a dry lubricant by (1) rotating a cylindrical soapbox; (2) vibrating the soapbox; and (3) using a special device which contains rotating rolls situated in the soapbox, such as the device produced by the Wire Lab Company, U.S.A., as Models LA-CW and LA-S.
The closest patent art pertinent to his invention of which the applicant is aware includes the following. U.S. Pat. No. 3,142,832 discloses the use of an additional die, called a "pressure die", which is located in front of the usual die. The pressure die has a diameter hole slightly greater than the wire diameter. U.S. Pat. Nos. 2,135,659 and 2,883,039 disclose the method of preliminary wire bending before entry into the soapbox to make the trajectory of the wire movement through the dry lubricant more circuitous. U.S. Pat. Nos. 2,349,652 and 3,763,680 disclose using a special die with a particular entrance angle which together with a high drawing speed feeds dry powdered lubricant into the reduction angle of the die by pseudohydrodynamic force. U.S. Pat. No. 3,703,449 discloses means for formation of lubricant coating on the wire by electrolysis.
Japanese published application No. 224814 to Misubishi Heavy Industries and Russian Patent No. 733755 to Refractory Met Allo show the use of magnets and magnetic lubricants. While these systems may provide some improvement, they suffer from various deficiencies. By way of example, the Japanese device utilizes a fixed magnet that is not adjustable and the Russian device utilizes a complex electromagnetic arrangement. Furthermore, the lubricants disclosed therein have not proven to be effective.
Using any of the above-described methods, does not solve the needs in the art of wire drawing which still require these attributes; reliable and sufficient feed of dry powdered lubricant into the die, a means for significantly reducing the cost of wire drawing, and finally a means for adjusting the quantity of lubricant fed into the die.